Antioxidants



May 1954 H. D. NORRIS ETAL 2,679,481

ANTIOXIDANTS Filed Feb. 7, 1952 2o 30 4o 50 60 70 60 70 700 7/0 I 0/06 Patented May 25, 1954 ANTIOIHDANTS Henry D. Norris, Woodbury, and Ralph V. White, Pitman, N. J assignors to Socony-Vacuum Oil Company, York Incorporated, a corporation of New Application February 7, 1952, Serial No. 270,303

7 Claims.

This invention relates, broadly, to lubricants containing organic nitrogen compounds. It s more specifically concerned with mineral lubr1- eating oils having improved resistance to oxidation.

As is well known to thos skilled in the art, most lubricants undergo a relatively rapid deterioration during use, as the result of the effects of oxidation. This oxidation is effected by a combination of factors, including relatively high temperatures and atmospheric oxygen. It is hastened, i. e., catalyzed, by metals, such as iron, copper, and copper alloys, which are present in lubrication systems. Oxidation of a lubricating oil is manifested by the formation of corrosive, acidic bodies, sludge, and high color. Especially highly refined lubricating oils, such as those used for lubricating steam turbines, are particularly susceptible to oxidation. That such action, together with its undesirable manifestations, cannot be tolerated in such engines, will be readily appreciated by those skilled in the art.

It has now been found that certain nitrogencontaining organic compounds effectively inhibit the oxidation of lubricants. It has now been discovered that mineral lubricating oils containing specific piperazine compounds are resistant to oxidation. In U. S. Patent No. 2,316,587, the use of diaryl piperazines to stabilize transformer oils is proposed. It has been found, however, that these compounds are not effective in the present invention, and are not contemplated within the scope of this invention.

Accordingly, it is a broad object of the present invention to provide lubricants having increased resistance to oxidation. Another object is to provide improved mineral lubricatingoils con taining organic nitrogen-containing compounds. A specific object is to provide mineral lubricating oils containing specific piperazine compounds, which oils have an increased resistance to oxidation. Other objects and advantages of this invention will become apparent to those skilled in the art, from the following detailed description.

The present invention provides a mineral lubricating oil containing a small amount, sufii- .cient to stabilize it against oxidation, of a compound selected from the group consisting of (1) compounds having the formula,

CHzCHz RN\ /NY onion, wherein R is a radical of the group consisting of ,3- (phenylamino) ethyl, ,9- (naphthylamino) ethyl, c-(o-tolylaminmethyl, and B-(m-tolylamino) ethyl radicals, and Y is a radical of the roup consisting of phenyl, naphthyl, o-tolyl, and m-tolyl radicals; and (2) compounds having the formula,

CH2CH2 CHzC 2 wherein R. is an alkyl radical having between one and 8 carbon atoms, and R is a radical of the group consisting of phenyl and naphthyl radicals and the radical having the formula,

CHzCHz The compounds having the formula,

267N112 (xomonom-nx In order to produce compounds which areefproperties of the compounds contemplated herein.

The compounds having the formula,

omen; RN N-R CHzCHj wherein R, and R" are as aforedescribed, are prepared by reacting a primary arylamine with a di(fi-haloethyl)alkylamine hydrohalide in a molar proportion of 1:1, respectively. As illustrated with aniline and di-(bromoethyl)methylamine h-ydrobromide, the reaction proceeds in accordance with the equation.

ONHZ (BrCHzCHmNCHa-HBr /onzom The di-(p-haloethyl) alkylamine hydrohalide reactant can contain between one and 8 carbon atoms per alkyl radical. The halogen atoms thereof can be bromo, chloro, or iodo atoms. Non-limiting examples of the alkyl radicals of these amines, which radicals can be straight chain or branched-chain, are methyl, propyl, isopropyl, ethyl, butyl, isobutyl, t-butyl, amyl, secamyl, hexyl, isoheptyl, octyl, and 2-ethylhexyl radicals. The primary aromatic amines which react with the dihaloethylalkylamine reactant, as aforedescribed, to form the additives of type (2) are aniline, naphthylamine, and 4,d'-diaminodiphenylmethane. Since there are two amino groups in the additive compound is prepared by reacting two moles of di-(p-haloethyl) alkylamine with each mole of 4,e'ediaminodiphenylmethane. As is the case of the aromatic amin reactants in Equation 1, these aromatic amines cannot have other substituent groups on the aromatic ring, without detracting from the anti-oxidant properties of the compounds produced therefrom. In the compounds illustrated by Equation 2, whenever there is an aryl group attached directly to one nitrogen atom of piperazine, there must be an allryl group of one to 3 carbon atoms attached to the other. In other words, diarylpiperazines are not effective in the present invention.

In both reactions illustrated by the Equations 1 and 2, it will be noted that hydrogen halide is a by-product of the reaction. In order to ensure complete reaction, in accordance with the principle of Le Chatelier, the hydrogen halide should be removed or chemically immobilized. This can be effected by having sufiicient hydrogen halide acceptor present in the reaction system to combine with the hydrogen halide. Amines are often used for this purpose, forming the amine hydrohalide. This amine can be an excessive latter amine which can react, the

' 2 per cent. Mineral amount of the aromatic amine reactant, or it can be another amine, preferably a tertiary alkylamine. Thus, in Equation 1, six moles of aniline could be used, i. e., two moles for the principal reaction and four moles to react with the hydrogen halide. Alternatively, at least four equivalents of a suitable hydrogen halide acceptor can be used. Suitable hydrogen halide acceptors include trialkylamines (tributylamine, triamylamine, triethylamine, etc.) heterocyclic nitrogen compounds (pyridine, piperidine, etc.) inorganic bases (sodium carbonate, sodium bicarbonate, etc), and many others well known to those skilled in the art.

The compounds utilized in this invention are prepared at temperatures of between about 160 C. and about 240 0., preferably between about 200 C. and about 230 C. The time of reaction varies, dependent on the temperature and the reactants involved, between about three hours and about 15 hours. Product separation can be effected by usual methods, including distilling and/or filtering off excess reactants and amine hydrohalide. The residue is the desired compound in a substantially pure form. This can be subjected to further purification steps well known to the art, e. g., extraction .or crystallization.

The piperazine compounds utilizable for the purposes of the present invention are blended in a mineral lubricating oil atv concentrations of between about 0.05 per cent, by weight, and about 5 per cent, by weight. Preferably the concentra tion varies between about 0.1 per cent and about oil concentrates of the additive compounds are contemplated. Thus, more than 5 per cent, by weight, and up to about 49 per cent of the additive (limited by the dispersibility thereof in mineral oil) could be blended in a mineral oil fraction. The resultant concentrate can be diluted, at any time prior -to use, with a suitable amount of the mineral lubricating oil to be inhibited, thereby achieving, ultimately, a mineral oil blend containing the desired amount of additive.

The following specific working examples are for the purpose of illustrating the additives contemplated herein and to demonstrate their effectiveness. This invention is not to 'be limited to the specific compounds used, or to the operations and manipulations involved therein. Other compounds, as described hereinbefore, can be used, as those familiar with the art will readily understand.

EFFECTIVE COM OUNDS Emample 1.-N- [,8- (am'lino) ethyl] -,N-ph,enylpiperazine Tri-(B-chloroethyl) amine hydrochloride (15 grams, 0.062 mole) and aniline (45 grams, 0.484 mole) were placed in a reaction vessel and heated at reflux temperatures for 3 hours. During the reflux period, the temperature of the reaction mixture rose from 185 C. to 210 C. The reaction mixture was cooled and made strongly basic ether. The ether solution was washed with water and dried over solid potassium hydroxide. The solution was filtered, and the ether was removed by evaporation over the steam bath, leaving 18 hours.

\ 9 hours.

grams of oily product. After this oil stood for a few days, crystals appeared. These were recrystallized from dilute alcohol, and were found to have a melting point of 58-59 C. In Rec. Trav.

.Chim., 56, 1007 (1937), van Alphen reported a refluxed for 6 hours at 216 C. The reaction mixture was cooled, and made distinctly alkaline with about 250 milliliters of a per cent, by weight, aqueous solution of sodium hydroxide. The mix ture was subjected to steam distillation until all of the tri-n-butylamine had been distilled out. The .residual ether (about Water. potassium hydroxide and filtered. The ether material was taken up in diethyl 250 milliliters) and washed with The ethereal solution was dried over solid was evaporated from the filtrate, over the steam bath. The product (19 grams thereof) was a dark-colored oil which contained no halogen, and

9.67 per cent nitrogen. Example 3.N-(1-naphthyl) -N'-7L-butZ/Z17ip67tlzine N,N-di(,6-chloroethyl) n butylamine hydrochloride, l-naphthylamine, and tri-n-butylamine, in a molar proportion of 1:1:3.3, respectively, were heated together at 210 C. for four hours. N-(l-naphthyl-N' n butylpiperazine was obtained from the reaction mixture in accordance with the method set forth in Example 2. The

- isolated product contained 9.1 per cent nitrogen.

Example 4.N-phenyl-N-n-butylpiperazine Aniline and N,N-di(,8-chloroethy1) -n-butylamine hydrochloride, in a molar proportion of 5:1, respectively, were reacted at 210 C. for 3.5

N -phenyl-N -n-butylpiperazine, containing 12.89 per cent nitrogen, was isolated as described in Example 1.

Example 5 .4,4 -dz' [1 4-n -butylpiperaeino) ldiphenylmethane N,N-di(,8-ohloroethyl) n butylamine hydrochloride, 4,4-diaminodiphenylmethane, and trin-butylamine, in a molar proportion of 2:1:7, re-

were refluxed together at 216 C. for The product, containing 11.16 per cent nitrogen, was isolated in accordance with the procedure set forth in Example 2. This compound has the structural formula:

CHzCHz spectively,

CH2OH2 Example 6'.-N- [p- (m-tolylamino) ethyl] -N'-mtolylpiperazine Tri-(fi-chloroethyl) amine hydrochloride, mtoluidine, and tri-n-butylamine, in a molar proportion of 1:2:4.5, respectively, were heated in a closed bomb for 12 hours at 230 C. N-LB-(mtolylamino) ethyl] -N-m-tolylpiperazine was obtained therefrom, in accordance with the procedure described in Example 2.

Example 7.-N-[p-(o-tolylamino) ethyl] N otolylpz'perazi e Tri-ifi-chloroethylamine hydrochloride, o-toluidine, and tri-n-butylamine, in a molar proportion of 1:2:45, respectively, were heated in a closed bomb at 230 .C. for 12 hours. N-[fi-(O- tolylamino)ethyl]-N'-otolylpiperazine was obtained therefrom, in accordance with the procedure described in Example 2.

INEFFECTIVE COMPOUNDS The following substituted piperazines were found to be ineffective for the purposes of this invention.

Examples 8 and .9.N-[,s-(p-t-amylphenylamino) ethyl] -N'- (p-t-amylphenyl) piperazine Tri-(p-chloroethyl) amine hydrochloride, p-tamylaniline, and tri-n-butylamine, in a molar proportion of 1:215, respectively, were heated together at 210 C. for 8 hours. Using the method of Example 2, N-[fi-(p-t-amylphenylamino) ethyl] N- (p-t-amylphenyl) piperazine was obtained from this reaction. In a second preparation, the same reactants in the same proportions were heated in a closed bomb for 12 hours at 230 C. The product was isolated as aforedescribed.

Example 10.N [e-(p-tolylamino) ethyl] -N'-ptolylpz'perazz'ne Tri (,B-chloroethyDamine hydrochloride, ptoluidine, and tri-n-butylamine, in a molar proportion of 1:2:45, were heated together in a closed bomb for 12 hours at 230 C. The product, N [,8 (p tolylamino) ethyl] N p tolylpiperazine, was isolated using the method described in Example 2.

Example 11 .N,N'-diphenylpz'perazine This compound was prepared by reacting aniline with ethylene bromide, in a molar proportion of 111.3, respectively, for 4 hours at 160 C.

Example 12. N,N'-0li(p-t-amylphenyl) piperazine This compound was obtained from the reaction of p-t-amylaniline, ethylene bromide, and sodium carbonate, in a molar proportion of 1:121, respectively, at 160 C., for 7 hours.

TEST DATA The base oil used in testing the aforedescribed compounds is a furfural refined Midcontinent (Rodessa) distillate stock. It has a specific gravity of 0.860, a flash point of 405 F., and a viscosity of 155 S. S. U. at F. This oil is suited for use in steam turbines.

Example 13 Each of the products of Examples 1 through 12 was blended in portions of the base oil at a Brown-Boveri Rev., 16 (2), 92-7 (1929). Briefly, a 200-milliliter sample of oil under test is placed in a IOU-milliliter V-shaped piece of polished copper. over the surface of the oil at a rate of two liters per hour. The test is conducted for 72 hours at 230 C. and then for 24 hours at room temperature. The results, in terms of condition of the copper, neutralization number (N.N.) and Lovibond color, indicate the oxidation stability of the oil. These results are compared with similar results for the uninhibited base oil. Pertinent test data for compounds of Examples 1 through '7 are set forth in Table I. Similar data for the Air is passed covered beaker containing a acidity is the primary ineffective compounds of Examples 8 through :12 are set forth in Table II.

Table I .--Brown-Boveri Turbine Oil Test ethyl] N tolylpipcrazine. l l

Neutralization number.

Table II.-Brown-Booeri Turbine Oil Test INEFFECTIVE COMPOUNDS BLENDED AT 0.2% CON CEXIRATI'ON IN OIL Example Compound Tested gg sg N..\'.* Copper Uninhibitcd Base Oil.

a mylphenylpiperzine.

10 N-[B-(p-tolylarnino) ethyl] N -p tolylpi- I, perazme.

i1 .4 N,I l"diphenylpiper- 7 azmc. l2 N,N-di(p-t-amyl- 9 1 phcnynpiperazine.

* Neutralization number.

Example 14 Some of the reaction products described in the preceding examples were subjected to the ASTM Turbine Oil Oxidation Test. This test is fully described in the ASTM Manual, as Test D-9i3- 47'1'. In general, the test involves placing a 300- rnilliliter sample of test oil in a tube provided with a gas inlet having a fritted glass outlet, and aica-talyst coil consisting of interwound iron and copper wire. The test is conducted at a temperature of 203:0.9" F. Sixty milliliters of water are maintained in the tube, and oxygen is passed through the oil at the rate of 3 liters per .hour. The test is contained until periodic testing shows that the oil has greatly increased in acidity, a sign of the formation of acidic oxidation products. These data are usually plotted graphically. Color can also be noted, although criterion in this test.

In addition to the uninhibited base oil, four blends were subjected to this test. Blend R. was a blend of 0.2 per cen by weight, of N-[c-(anilino) -ethyll -Nphenylpiperazine (Example 1) in the base oil. Blend S comprised 0.2 per cent, by weight, of N-phenyl-N'-n-butylpiperazine (Example 4) in the base oil. Blend T comprised the base oil containing 0.2 per cent, by weight, of a4 -di l l-n-butylpiperazino) diphenyl-meth-- ane (Example 5). Blend U was a blend of 0.2 per cent, by weight, of N,N-di(p-t-amylphenyl piper- -aaine (Example 12) in the base oil. Pertinent test results for these blends are set forth in Table III.

- In the case of blend T, the acidity Table I II .-ASTM Turbine Oil Oxidation Test [(0.2% by weight of compound'in base 011)] Color,

Example Compound Tested Hours Days govii N.N.'

24 1 s 0.05 Uninhibited Base Oil. 48 2 14 0.92

qa it? it "1% 11?? Nmphenylplpem' 11912 79 24 2. 2

Z i O I {as a a2 is; Pipelazme- 1, 176 49 185 1e. 3

5 iii; 13% i 0.36 Plperazmo) 3:624 151 7 0.60 Phenylmethane- 3, 728 155 260 10. 7

12 N,N-di(p-t-amyl- 72 3 s 0.8 phenyl) piperazine. 144 6 330 10. 6

Neutralization number.

In Figure 1, the acidity (N.N.) data for the tests reported in Table III are plotted graphically. As will be apparent from the curve for the base oil (curve A), uninhibited oils rapidly undergo oxidation. Curve A is a typical curve, in that the acidity remains low until oxidation commences. At that point, acidity increases rapidly, often within a matter of a few hours, causing a sharp rise in the curve. It will be noted that blend R maintained a low acidity throughout more than 42 days. It was not until almost days had passed that the acidity increased. Test blend S lasted for about 49 days before acidity increased. remained low for about days, and did not rise tremendously until about 5 days later. As compared with the foregoing, blend U lasted only 6 days on the ASTM Oxidation Test, indicating that the oxidation inhibition was very insignificant. It will be noted that this blend did not last much longer than the uninhibited base oil.

In the foregoing examples, the efiectiveness of the compounds contemplated herein has been demonstrated. It will be appreciated that this relatively narrow class of substituted piperazine compounds is effective, when added to lubricating oils in small amounts, in inhibiting the oxidation thereof. It should be noted that when the compound has an aryl group directly attached to one nitrogen atom of the piperazine nucleus, the other nitrogen atom must have an alkyl group attached thereto. This can be appreciated by comparing the compounds of Examples 3 and 4 with the compounds of Examples 11 and 12.

Gther oil addition agents can be used along with the additives of this invention, to improve other characteristics of the oil. For example, antirust agents, oiliness agents, E. P. agents, V. I. improvers, pour point depressants, detergents, antifoamants, and the like can be added to the mineral lubricating oil along with the additives of this invention. Such other additives are well known to those familiar with the art. Accordingly, it is believed unnecessary to list them here.

Although the present invention has been described in conjunction with preferred embodiments, modifications and variations are contemplated, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.

Vfhat is claimed is:

i. A solvent-refined mineral steam turbine lubricating oil containing a small amount, suffic-ien-t to stabilize it 'against oxidatiomof ai-compound selected from the group consisting of (1) compounds having the formula,

omen:

wherein R is a radical of the group consisting of p- (phenylamino) ethyl, fi- (naphthylamino) ethyl,

(o-tolylamino) ethyl, and 5- (m-tolylamino) ethyl radicals, and Y is a radical of the group consisting of phenyl, naphthyl, o-tolyl, and mtolyl radicals; and (2) compounds having the formula,

wherein R" is an alkyl radical having between one and 8 carbon atoms, and R is a radical of the group consisting of phenyl and naphthyl radicals and the radical having the formula,

OH2CH2 2. A solvent-refined mineral steam turbine lubricating oil containing between about 0.05 per cent by weight and about 5 per cent by weight of a compound selected from the group consisting 01 1) compounds having the formula,

10 m-tolyl radicals; and (2) compounds having the formula,

CHzCH:

wherein R" is an alkyl radical having between one and 8 carbon atoms, and R is a radical of the group consisting of phenyl and naphthyl radi- 10 cals and the radical having the formula,

CHzCHz 15 3. A solventrefined mineral steam turbine lubricating oil containing a small amount, sufiicient to stabilize it against oxidation, of N-[B-(anilino) -ethyl] -N '-pheny1piperazine.

i. A solvent-refined mineral steam turbine lu- 0 bricating oil containing a small amount, suficient to stabilize it against oxidation, of N-[fi-(lnaphthylamino) ethyll-N' (1 naphthyDpiperazine.

5. A solvent-refined mineral steam turbine lu- 5 bricating oil containing a small amount, sufl'icient to stabilize it against oxidation, of N-(l-naphthyl) -N-n-butylpiperazine.

6. A solvent-refined mineral steam turbine lubricating oil containing a small amount, sufficient 39 to stabilize it against oxidation, of N-phenyl-N'- n-butylpiperazine.

7. A solvent-refined mineral steam turbine lubricating oil containing a small amount, sufiicient to stabilize it against oxidation, of 4,4'-di[1-(4- 5 n-butylpiperazino) ldiphenylmethane.

References Cited in the file of this patent UNITED STATES PATENTS Name Date 0 Number Irigai Apr. 13, 1943 

1. A SOLVENT-REFINED MINERAL STEAM TURBINE LUBRICATING OIL CONTAINING A SMALL AMOUNT, SUFFICIENT TO STABILIZE IT AGAINST OXIDATION, OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF (1) COMPOUNDS HAVING THE FORMULA, 